[en] We have designed and developed novel luminescent lanthanide complexes based on a coumarin derivative, using a new promising synthetic method developed in our laboratory. The unsaturated 6-coordinated complexes coordinated with three H₂O molecules were formed. The present Er(III)- and Eu(III)-chelated complexes showed an intra 4f shell electronic transition from its first excited state to the ground state taking place at 1530 and 614 nm, respectively. The stronger emission intensity was obtained by the photoexcitation of the coumarin-based ligand with the wavelength of 325 nm rather than by the direct photoexcitation of the lanthanide ions. It could be explained by the fact that the effective energy transfer between the coumarin ligand and the lanthanide ions takes place.

[en] Rare-earth-doped phosphors for near ultraviolet excitation are under an extensive research for applications to white-light-emitting diodes. In this study, we prepare red-orange emitting samariumdoped rhombohedral tricalcium phosphate particles by using the solid-state reaction method. The synthesis procedures are reported, the formation of prepared particles is confirmed using X-ray diffraction patterns, and the morphology and the elemental composition are measured using a scanning electron microscope. We also investigate the photophysical properties of trivalent samariumdoped tricalcium phosphate phosphors by taking absorption, excitation, and emission spectra at room temperature. We show that the trivalent samarium-doped tricalcium phosphate phosphors are red-emitting phosphors and have higher efficiency with near ultraviolet excitation. The emission intensity increases very sharply up to a samarium concentration of 2.5 mol% and then decreases as the concentration increases. Therefore, the samarium doping concentration in the tricalcium phosphate phosphor needs to be optimized.

[en] ZnO-branched nanostructures have recently attracted considerable attention due to their rich architectures and promising applications in the field of optoelectronics. Contrary to n-type semiconducting metal oxides, cupric oxide is a p-type semiconductor which can be applied to high-critical-temperature superconductors, photovoltaic materials, field emission, and catalysis. We report the synthesis of the ZnO nanorods on the CuO nanofibers prepared by using the electrospinning method along with the hydrothermal method. As the growing time increases, emission spectra of the hetero-structured ZnO/CuO show that the observed band in the UV region is slightly increased, while the intensity of the green emission is highly enhanced. The hetero-structured ZnO/CuO is found to be a promising candidate for developing renewable devices with photoluminescent behavior and the increased surface to volume ratio.

[en] Rare-earth-doped phosphors for near ultraviolet excitation are under an extensive research for applications to white-light-emitting diodes. In this study, we prepare red-orange emitting samarium-doped rhombohedral tricalcium phosphate particles by using the solid-state reaction method. The synthesis procedures are reported, the formation of prepared particles is confirmed using X-ray diffraction patterns, and the morphology and the elemental composition are measured using a scanning electron microscope. We also investigate the photophysical properties of trivalent samarium-doped tricalcium phosphate phosphors by taking absorption, excitation, and emission spectra at room temperature. We show that the trivalent samarium-doped tricalcium phosphate phosphors are red-emitting phosphors and have higher efficiency with near ultraviolet excitation. The emission intensity increases very sharply up to a samarium concentration of 2.5 mol% and then decreases as the concentration increases. Therefore, the samarium doping concentration in the tricalcium phosphate phosphor needs to be optimized.

[en] We have prepared ZnO nanofibers by using the electrospinning method and have analyzed the variations in their structure, optical properties, and chemical bonding states with the annealing temperature and the annealing conditions. After annealing at 500 .deg. C, the average diameter and the average grain size are determined to be approximately 170 nm and 50 nm, respectively. The ZnO nanofibers have a clearly visible dislocation-free crystal structure. The 2p level of Zn caused Zn-O bonds and the O 1s core level caused physisorbed O₂. When the nanofibers are annealed at 700 deg C, both ions exhibit shifts of the binding energies compared with those annealed at 500 .deg. C. The observed band in the visible region shows a strong temperature dependence and a red-shift with the oxygen flow in annealing process, which is related to oxygen vacancies.

[en] Magnesium ferrite (MgFe2O4) exhibiting a spinel phase was synthesized by using the polymerized complex and the solid-state reaction methods, and its physico-chemical properties were studied to explore the water-splitting under visible light photons. The study revealed the potential for using MgFe2O4 particles for photo-catalytic application. The structural study provided information on ferrite nano-crystallites fabricated by using the polymer complex method. The morphological studies demonstrated that, in contrast to the solid-state reaction method, a homogenous, monodispersed ferrite photocatalyst could be formed by using the polymerized complex method. The optical study revealed a larger visible-light absorption capability for the nanosized MgFe2O4 photocatalysts prepared by using the polymer complex methods, and indicated a red-shift of the bandgap by 0.06 eV as compared to the bandgap of the bulk. These nanocrystallites were highly photoactive with respect to the photodegradation and photocatalytic hydrogen evolution applications. The electrochemical analysis showed that they exhibited favorable bandedge positions suitable for photocatalytic H2 evolution. Thus, nanocrystalline MgFe2O4 is an active visible-light photocatalyst, that might be useful for the decomposition of water.

[en] The synthesis of narrowly dispersed nanocrystalline TiO₂ was investigated with a surfactant aided solvothermal synthetic method in toluene solutions. When a sufficient amount of titanium isopropoxide, Ti[OCH(CH₃)₂]₄ (TIP), was added to the solution, the shapes of TiO₂ nanoparticles changed from spheres to rods. The aggregated microstructures of the nano-sized TiO₂ in systems of spheres, rods, and mixtures of spheres and rods was studied using TEM. The morphological shape of the aggregation was described in terms of the fractal dimensions. We used a box-counting method to get the fractal dimension of these systems. The fitted fractal dimensions for spheres, sphere/rod mixtures, and rods are D = 1.54, D = 1.81, and D = 1.89, respectively. The fractal dimension changed from 1.54 to 1.9 with the TIP/toluene ratio, indicating that the growth mechanism for aggregations showed different behaviors.

[en] Highlights: • EDTA was introduced into PAA to suppress the HF creation. • PAA/EDTA binder derived an exceptional cycling performance. • Si-PAA/EDTA electrode showed good thermal stability after temperature storage. The crucial roles of ethylenediaminetetraacetic acid (EDTA) in the poly(acrylic acid) (PAA)-binder system were investigated for the high electrochemical performance silicon anode in lithium-ion batteries. The EDTA supports the construction of a mechanically robust network through the formation of sbndCOOH linkage with the SiO₂ layer of the Si nanoparticles. The mixture of the PAA/EDTA binder and the conductive agent exhibited an improved elastic modulus and peeling strength. The creation of hydrogen fluoride (HF) was effectively suppressed through the elimination of the H₂O. An H₂O–phosphorous pentafluoride (PF₅) reaction, which is known for its use in the etching of metal oxides including its creation of the solid electrolyte interphase (SEI) layer, generates the HF. A remarkably sound cyclability with a discharge capacity of 2540 mA h g⁻¹ was achieved as a result of the synergistic effect between robust mechanical properties and suppression of the HF creation for the stability of the SEI layer.

[en] Nanocrystalline TiO₂ powders were obtained by the solvothermal route from the Ti(OR)₄ precursor precipitated in toluene under different concentrations. The prepared titania is in the form of nanocrystalline anatase with different sizes dependent on the precursor concentrations. Average particle size is about 10 nm and 20 nm for contents of precursor below 10 mol% and above 50 mol%, respectively. TiO₂ nanoparticles tend to agglomerate to form sphere balls from the solutions of above 20 mol% concentration. Dependence of particle size on the anatase-rutile phase transformation was investigated by XRD study. Morphology of titania particles depending on annealing temperature was also investigated using scanning electron microscopy